Abstract. The historical total ozone measurements taken with Dobson Spectrophotometer #8 at Longyearbyen, Svalbard, Norway, in the period 1950–1962 have been re-analyzed and homogenized based on the original measurement logs, using updated relevant parameters. In lack of sufficient calibration information, an empirical quality assessment was performed, based on a climatological comparison with ozone measurements in Tromsø, using TOMS data at both sites in the period 1979–2001, and Dobson data in the period 1950–1962. The assessment revealed that, as in the case of the Tromsø measurements, the C wavelength pair direct-sun measurements are most trustworthy (and most frequent), while the WMO standard reference mode AD direct-sun has a systematic bias relative to this data set. Zenith-blue (ZB) measurements at solar zenith angles (SZA) <80° were homogenized using two different polynomials before and from 1957; also ZB measurements at larger SZAs were homogenized by means of a normalization function derived from days with measurements over a wide range of SZAs. CC' zenith-cloudy measurements, which are particularly frequent during the summer months, were homogenized by applying correction factors for only two different cloud types: high thin clouds and medium/low/thick clouds; a further diversification of corrections reflecting cloud conditions did not prove significant. The combination of all measurements yields a total of 4837 single values, covering 1676 days from September 1950 to September 1962; moon measurements during the polar night add another 137 daily means. The re-evaluated data show a convincing agreement with measurements since 1979 (TOMS, SAOZ, Dobson) as well as with the 1957–1962 data stored at the World Ozone and UV Data Centre (WOUDC).
Total ozone trends at sixteen NOAA/CMDL and Cooperative Dobson Spectrophotometer Observatories during 1979-1996
